71 lines
3.6 KiB
C
71 lines
3.6 KiB
C
#ifndef _PROCFS_TYPE_H
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#define _PROCFS_TYPE_H
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typedef void *data_t; /* abstract data type; can hold pointer */
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/* ProcFS supports two groups of files: dynamic files, which are created within
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* process-specific (PID) directories, and static files, which are global. For
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* both, the following structure is used to construct the files.
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*
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* For dynamic files, the rules are simple: only regular files are supported
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* (although partial support for symbolic links is already present), and the
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* 'data' field must be filled with a pointer to a function of the type:
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*
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* void (*)(int slot)
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*
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* The function will be called whenever a read request for the file is made;
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* 'slot' contains the kernel slot number of the process being queried (so for
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* the PM and VFS process tables, NR_TASKS has to be subtracted from the slot
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* number to find the right slot). The function is expected to produce
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* appropriate output using the buf_printf() function.
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*
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* For static files, regular files and directories are supported. For
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* directories, the 'data' field must be a pointer to another 'struct file'
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* array that specifies the contents of the directory - this directory will
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* the be created recursively. For regular files, the 'data' field must point
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* to a function of the type:
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*
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* void (*)(void)
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*
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* Here too, the function will be called upon a read request, and it is
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* supposed to "fill" the file using buf_printf(). Obviously, for static files,
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* there is no slot number.
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*
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* For both static and dynamic files, 'mode' must specify the file type as well
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* as the access mode, and in both cases, each array is terminated with an
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* entry that has its name set to NULL.
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*/
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/* The internal link between static/dynamic files/directories and VTreeFS'
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* indexes and cbdata values is as follows:
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* - Dynamic directories are always PID directories in the root directory.
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* They are generated automatically, and are not specified using a "struct
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* file" structure. Their index is their slot number, so that getdents()
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* calls always return any PID at most once. Their cbdata value is the PID of
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* the process associated with that dynamic directory, for the purpose of
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* comparing old and new PIDs after updating process tables (without having
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* to atoi() the directory's name).
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* - Dynamic files are always in such a dynamic directory. Their index is the
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* array index into the "struct file" array of pid files (pid_files[]). They
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* are indexed at all, because they may be deleted at any time due to inode
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* shortages, independently of other dynamic files in the same directory, and
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* recreating them without index would again risk possibly inconsistent
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* getdents() results, where for example the same file shows up twice.
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* VTreeFS currently does not distinguish between indexed and delatable files
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* and hence, all dynamic files must be indexed so as to be deletable anyway.
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* - Static directories have no index (they are not and must not be deletable),
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* and although their cbdata is their associated 'data' field from their
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* "struct file" entries, their cbdata value is currently not relied on
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* anywhere. Then again, as of writing, there are no static directories at
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* all.
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* - Static files have no index either (for the same reason). Their cbdata is
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* also their 'data' field from the "struct file" entry creating the file,
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* and this is used to actually call the callback function directly.
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*/
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struct file {
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char *name; /* file name, maximum length PNAME_MAX */
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mode_t mode; /* file mode, including file type */
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data_t data; /* custom data associated with this file */
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};
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#endif /* _PROCFS_TYPE_H */
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